Radicals Are Required for Thiol Etching of Gold Particles

Etching of gold with an excess of thiol ligand is used in both synthesis and analysis of gold particles. Mechanistically, the process of etching gold with excess thiol is unclear. Previous studies have obliquely considered the role of oxygen in thiolate etching of gold. Herein, we show that oxygen or a radical initiator is a necessary component for efficient etching of gold by thiolates. Attenuation of the etching process by radical scavengers in the presence of oxygen, and the restoration of activity by radical initiators under inert atmosphere, strongly implicate the oxygen radical. These data led us to propose an atomistic mechanism in which the oxygen radical initiates the etching process.     

Detection of Heavy Metal Ions Using Synthesized Amino Thiol Surfactants Assembled on Gold Nanoparticles

In this work, we synthesized amino thiol surfactants, namely, 10-(4-aminophenoxy)-decane-1-thiol and 12-(4-aminophenoxy)-dodecane-1-thiol. The self-assembling of the synthesized surfactants on gold nanoparticles (AuNPs) was investigated using different techniques such as ultraviolet analysis, x-ray diffraction, and transmission electron microscopy. The synthesized surfactants show the ability to assemble on gold nanoparticles and form stable nanostructure with it. We used the synthesized surfactants and their nanostructures with gold nanoparticles for the detection of Zn and Ni ions in aqueous solution using the ultraviolet spectrophotometer technique. The synthesized amino thiol surfactants showed the ability to detect Zn and Ni ions at low concentration. The results showed that gold nanoparticles can enhance the detection of Zn and Ni ions using the nanostructures of the synthesized surfactants.     

Characterization of Formation Kinetics of Self-Assembled Thiol Monolayers on Gold by Electrochemical Impedance Spectroscopy

Interest in the properties of organized monolayers has grown enormously in recent years because these monolayers can provide a means to control the interface at a molecular level1. The self-assemblies of alkanethiols and their derivatives were probably the most intensively studied due to their stability, well-packed structure, ease in preparation, and flexibility in designing the tail group2. The adsorption kinetics of thiol monolayer has been studied by using several techniques, including con…     

Synthesis and Characterization of Self-Assembling Some Thiol Surfactants on Gold Nanoparticles

The purpose of this work is to study the self-assembling of some synthesized thiol surfactants namely (mercaptopropane-, mercaptohexane-, mercaptooctane-, and mercaptodecane sodium sulfonate) on the fabricated gold nanoparticles. The self-assembling of these surfactants on gold nanoparticles characterized using different techniques such as FTIR spectroscopy, UV spectroscopy, and transmission electron microscopy (TEM). Spectroscopic evidence suggests that the synthesized thiol surfactants have been attached to the gold nanoparticles. The effect of self-assembling of these surfactants on the size of the gold nanoparticles was studied using TEM images. The growth of the gold nanoparticles was investigated with respect to the increase of alkyl chain in the synthesized thiol surfactants. The results show that the stabilization of gold nanoparticles was affected by the increase in alkyl chain length of these surfactants. The effect of gold nanoparticles on the interfacial tension and the emulsion stability of these surfactants with crude oil was studied.     

Studies on the Hydrogen Transfer Reaction Mechanism of Singlet Thiol Phosphinidene Complex and the Temperature Effect

The hydrogen transfer reaction mechanism of the complex of a singlet thiol phosphinidene and a polar molecule hydrogen fluoride (HSP- - - HF) has been investigated at the B3LYP/6-311+G (d,p) level in order to better understand the reactivity of singlet phosphinidene. The results show that the relevant reaction, including step 1 [HSP- - -HF(1) → TS1 (2) → HSPH(F) (3)] and step 2 [HSPH(F) (3) → TS2 (4) → H₂SPF (5)], are very different from the reactions of hydroxyl phosphinidene with hydrogen fluoride. Furthermore, theoretical studies on the thermodynamic and kinetic properties of the reaction have been carried out over the temperature range of 200–1200 K using the DFT/B3LYP method, the general statistical thermodynamics, and Eyring transition state theory with Wigner correction, which is used to examine the temperature effects the reaction channel. It is concluded that step 1 has both thermodynamic and kinetic advantages over step 2, and the high temperature is favorable to step 2. Moreover, the order of lgK and lgk for the steps are consistent with the order of their exoergic energies ΔE and barrier height, but the differences of lgK and lgk for the steps decrease with the temperature increases.     

Cyclometalated Gold(III)-Hydride Complexes Exhibit Visible Light-Induced Thiol Reactivity and Act as Potent Photo-Activated Anti-Cancer Agents

The specific gold-sulfur binding interaction renders gold complexes as promising anti-cancer agents that can potentially overcome cisplatin resistance; while their unbiased binding towards non-tumoral off-target thiol-proteins has posed a big hurdle to clinical application. Herein we report that cyclometalated gold(III) complexes bearing hydride ligands are highly stable towards thiols in the dark but can efficiently dissociate the auxiliary hydride moiety and generate a gold-thiol adduct when excited with visible light. In consequence, the photo-activated gold(III) complexes potently inhibited thioredoxin reductase in association with up to >400-fold increment of photocytotoxicity (vs. dark condition) without deactivation by serum albumin and along with strong anti-angiogenesis activity in zebrafish embryos. Importantly, the gold(III)-hydride complexes could be activated by two-photon laser irradiation at the phototherapeutic window as effectively as blue-light irradiation.     

Amperometric L‐cysteine Sensor Using a Gold Electrode Modified with Thiolated Catechol

A thiolated catechol (CA) consisting of 1,6‐Hexanedithiol (HDT) and CA was modified on a gold (Au) electrode to obtain an amperometric L‐cysteine sensor with detection limit of 60.6 nM. The preparation of thiolated CA was conducted via a thiol addition between HDT and electro‐oxidized CA (EOCA). Briefly, the thiol addition reaction was accomplished by potential cycling of HDT/Au electrode in 0.1 M phosphate buffer (PB, pH 7.2) containing CA, and an EOCA‐HDT/Au electrode was produced. The obtained EOCA‐HDT/Au electrode exhibits a pair of well‐defined redox peaks (at 0.22/0.10 V) of o‐quinone moiety, which effectively mediates the oxidation of L‐cysteine in a 0.1 M PB (pH 7.2), with an over‐potential decrease by ca. 0.12 V (versus bare Au electrode). Electrochemical quartz crystal microbalance, cyclic voltammetry and surface‐enhanced Raman spectra were used to study relevant processes and/or film properties. The amperometric L‐cysteine sensor has good anti‐interferent ability and reproducibility. It also has acceptable recovery for detection of L‐cysteine in urine samples.     

Mechanism and Cellular Kinetic Studies of the Enhancement of Antioxidant Activity by Using Surface‐Functionalized Gold Nanoparticles

The enhanced antioxidant activity of surface‐functionalized gold nanoparticles (AuNPs) synthesized by self‐assembly has attracted great attention, but little is known about the mechanism behind the enhanced activity. To address this challenge, the antioxidant activity of Au@PEG3SA (i.e., surface‐functionalization of spherical AuNPs with the antioxidant salvianic acid A) was used as an example to illustrate the mechanism of the enhanced activity. Evaluation of the antioxidant activity was performed in a radical‐scavenging reaction between Au@PEG3SA and 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical. As expected, the rate constant for the reaction of Au@PEG3SA with DPPH was about nine times greater than that for the salvianic acid A monomer. A comparative analysis of the spectral characteristics of Au@PEG3SA and the salvianic acid A monomer further imply that the enhancement of the antioxidative reaction kinetics may be ascribed to the variation in the transition state for the DPPH‐radical scavenging reaction through π–π stacking interactions between and among adjacent groups on the surface of Au@PEG3SA. On the other hand, the kinetic enhancement of Au@PEG3SA on reactive‐oxygen‐species (ROS) scavenging can be observed in living cells and in vivo, which possibly provides new insight for the bioapplication of self‐assembly of surface‐functionalized AuNPs.     

Preparation of Langmuir/Blodgett-cellulose Surfaces by Using Horizontal Dipping Procedure. Application for Polyelectrolyte Adsorption Studies Performed with QCM-D

A method of preparing model cellulose surfaces by the Langmuir–Blodgett (LB) technique with horizontal dipping procedure has been developed. The primary aim for the use of these surfaces was adsorption studies performed with the quartz crystal microbalance with dissipation (QCM-D) instrument. Hydrophobised cellulose (trimethylsilyl cellulose, TMSC) was deposited on the hydrophobic, polystyrene-coated QCM-D crystal. After 15 dipping cycles, the TMSC film fully covers the crystal surface. TMSC can easily be hydrolysed back to cellulose with acid hydrolysis. With this method a smooth, rigid, thin and reproducible cellulose film was obtained. Its morphology, coverage, chemical composition and wetting was further characterised using atomic force microscopy (AFM), X-Ray photoelectron spectroscopy (XPS), and contact angle measurements. The swelling behaviour and the stability of the cellulose film in aqueous solutions at different ionic strengths were studied using the QCM-D instrument. The swelling/deswelling properties of the cellulose film were those expected of polyelectrolytes with low charge density; some swelling occurred in pure water and the swelling decreased when the ionic strength was increased. No significant layer softening was detected during the swelling. The effect of electrolyte concentration and polymer charge density on the adsorption of cationic polyelectrolytes on the cellulose surface was also investigated. At low electrolyte concentration less of the highly charged PDADMAC was adsorbed as compared to low charged C-PAM. The adsorbed amount of PDADMAC increased with increasing ionic strength and a more compact layer was formed while the effect of electrolyte concentration on the adsorption of C-PAM was not as pronounced.     

基于发光金纳米粒子荧光增强法测定溶菌酶

参照文献方法合成了BSA修饰的水溶性发光金纳米粒子,并考察了其与溶菌酶之间的相互作用.依据溶菌酶对金纳米粒子的发光增强现象,建立了测定溶菌酶的荧光新方法.考察了发光金纳米粒子的浓度、pH值、反应时间及共存物质对测定的影响.优化条件为:发光金纳米粒子浓度4.0×10(-6)mol/L,pH 7.0、反应时间10 min....     

Gold Microelectrodes Decorated by Spike-Like Nanostructures as a Promising Non-Enzymatic Glucose Sensor

Gold microelectrodes modified via easy method by gold nanostructures were studied as an ideal substrate for non-enzymatic glucose detection. The results confirmed that spike-like nanostructure displays the best electrocatalytic activity because of higher amount of edges. Results prove that modified electrode is able to detect glucose in two linear ranges from 100–500 μM and 0.5–30 mM, with limit of detection (48 μM), high sensitivities for both linear ranges (1.7 μA/mM and 2.4 μA/mM), and good stability. In addition, modified electrodes were able to detect glucose in blood serum. This work demonstrates glucose detection on miniaturised system.     

Cyclometalated Gold(III)‐Hydride Complexes Exhibit Visible Light‐Induced Thiol Reactivity and Act as Potent Photo‐Activated Anti‐Cancer Agents

The specific gold‐sulfur binding interaction renders gold complexes as promising anti‐cancer agents that can potentially overcome cisplatin resistance; while their unbiased binding towards non‐tumoral off‐target thiol‐proteins has posed a big hurdle to clinical application. Herein we report that cyclometalated gold(III) complexes bearing hydride ligands are highly stable towards thiols in the dark but can efficiently dissociate the auxiliary hydride moiety and generate a gold‐thiol adduct when excited with visible light. In consequence, the photo‐activated gold(III) complexes potently inhibited thioredoxin reductase in association with up to >400‐fold increment of photocytotoxicity (vs. dark condition) without deactivation by serum albumin and along with strong anti‐angiogenesis activity in zebrafish embryos. Importantly, the gold(III)‐hydride complexes could be activated by two‐photon laser irradiation at the phototherapeutic window as effectively as blue‐light irradiation.     

Synthesis of Thiol Esters by the Reaction of Ricinoleic Acid with Thiols Under Solvent-Free Conditions

The synthesis of several ricinoleic acid thiol esters starting from cis-(R)-12-hydroxyoctadec-9-enoic acid and thiols in the presence of N,N′-dicyclohexylcarbodiimide (DCC) is described. The method is efficient for aromatic and aliphatic thiols, selectively affording the respective fat acid thiol esters in good yields under mild, neutral, and solvent-free conditions. The protocol is general and was extended to other carboxylic acids, furnishing the desired products in satisfactory yields. The (R,Z)-12-hydroxy-octadec-9-enylic acid benzylthiol ester 3a was successfully reduced to (R,Z)-12-hydroxyoctadec-9-enal 4.      

Spectrophotometric Label-Free Determination of Lead Using Thiol-Functionalized Gold Nanoparticles

A method for the determination of lead is described using thiol-functionalized gold nanoparticle. The detection method is based on the prevention of thiol-induced aggregation of gold nanoparticles by lead. Among six thiols, e.g., 4-mercapto-1-butanol, meso-2, 3-dimercaptosuccinic acid, mercaptosuccinic acid, 6-mercapto-1-hexanol, 4-(methylthio)-1-butanol, 1-propanethiol, four (4-mercapto-1-butanol, 6-mercapto-1-hexanol, 4-(methylthio)-1-butanol and 1-propanethiol) induced the aggregation of the gold nanoparticles which was measured by the change in absorbance at 520 and 650?nm. Prior incubation of the gold nanoparticles with lead decreased the 4-(methylthio)-1-butanol-induced aggregation of gold nanoparticles in a dose-dependent manner. A linear inverse relationship between the logarithmic concentration of lead and the ratio of absorbance at 650 to 520 was noted. The method has a dynamic range from 10?nM to 100?µM. However, metals such as mercury and chromium were more effective in comparison with lead in preventing the 4-methylthio-1-butanol-induced aggregation of gold nanoparticles. The method can be used for assessing the heavy metal load in water samples.     

Fusion and Growth Behavior of Gold Nanoparticles Stabilized by Allylmercaptane

Fusion and growth behavior of gold nanoparticles in a relatively low temperature range were studied using a transmission electron microscopy (TEM). Using allylmercaptane (AM: 2-propene-1-thiol, HS CH₂ CHCH₂) as a particle stabilizer, a colloidal suspension of AM-terminated gold nanoparticles was prepared with a two-phase system. TEM observation revealed that the adjacent nanoparticles formed a particulate neck to give fused nanoproducts even at lower than 65 °C. Such fusion behavior allowed a non-spherical growth of the adjacent nanoparticles. Interestingly, the nanoparticle fused to form a nanowire-type structure when the thermal radical reaction occurred between the terminal double carbon bond of the stabilizer and the hydrogen terminated surface of silicon wafer.     

Adsorption of polyelectrolyte multilayers and complexes on silica and cellulose surfaces studied by QCM-D

The adsorption of polyelectrolyte (PE) multilayers and complexes, obtained from both high- and low-charge polyelectrolytes, was studied on silica and on cellulose model surfaces by quartz crystal microbalance with dissipation (QCM-D). The film properties acquired with the different strategies were compared. When polyelectrolytes were added on an oppositely charged surface in sequence to form multilayers both the change in frequency and dissipation increased. The changes in frequency and dissipation were clearly higher if low-charge PEs were used in the multilayer formation. The substrate, silica or cellulose, did not affect the adsorption behaviour of low-charge PEs and only minor differences were seen in the adsorbed amounts and changes in dissipation of high-charge PEs between SiO₂ and cellulose. The complexes formed by low-charge PEs had higher changes in frequency and dissipation at low ionic strength on both surfaces, while the complexes formed from high-charge polyelectrolytes adsorbed more at high salt concentration. The complexes of low-charge polyelectrolytes adsorbed more on silica, while the complexes formed by high-charge PEs formed thicker layers on cellulose. The charge ratio had a significant effect on the adsorption and the highest changes in frequency and dissipation were obtained in the anionic/cationic charge ratio of 0.5–0.6. Generally, the multilayers and complexes formed by low-charge polyacrylamides adsorbed highly and formed rather thick layers on both surfaces, unlike the high-charge PEs which formed thin layers using either one of the addition techniques.     

利用去湿现象制备图案化的离子刻蚀聚合物保护层

微米和纳米尺度的图案化表面的制备在微电子、光学、生物、化学和材料科学等领域具有重要的科学意义和应用价值 [1～ 3 ] .由于需要复杂昂贵的设备和苛刻的工作环境 ,光刻技术难以广泛应用于微电子以外的领域 ,因此 ,发展简单、便宜、适用于普通实验室 (尤其是化学实验室 )的表面图案化技术已成为一个涉及众多学科领域的课题 .在近年来不断涌现出来的物理、化学和生物的表面图案化技术 [4～ 6]中 ,最具代表性的是由 Whitesides等 [7]发明的以表面具有微观图案的聚二甲基硅氧烷 (PDMS)弹性体作为模具或印章的软光刻技术 .结合溶胶 -凝胶、…     

Studies on the reaction between reduced riboflavin and selenocystine

Selenocysteine (Sec) is a crucial component of mammalian thioredoxin reductase (TrxR) where it serves as a nucleophile for disulfide bond rupture in thioredoxin (Trx). Generation of the reduced state of Sec in TrxR requires consecutive two electron transfer steps, namely: (i) from NADPH to flavin adenine dinucleotide, (ii) from reduced flavin to the disulfide bond Cys⁵⁹‐S‐S‐Cys⁶⁴, and finally (iii) from Cys⁵⁹ and Cys⁶⁴ to the selenosulfide bond Cys⁴⁹⁷‐S‐Se‐Sec⁴⁹⁸. In this work, we studied the reaction between reduced riboflavin (RibH2) and selenocystine (Sec‐Sec), an oxidized form of Sec. The interaction between RibH2 and Sec‐Sec proceeded relatively slowly in comparison with its reverse reaction, that is, reduction of riboflavin (Rib) by Sec. The rate constant for the reaction between RibH2 and Sec‐Sec was (7.9 ± 0.1) × 10^?2 M^?1 s^?1 (pH 7.0, 25.0°C). The reaction between Rib and Sec proceeded via two steps, namely, a rapid reversible binding of Rib to Sec having a protonated selenol group to form a Sec‐Rib complex, followed by nucleophilic attack of Sec‐Rib by a second Sec molecule harboring a deprotonated selenol group. The equilibrium constant for the overall reduction process of Rib by Sec is (1.2 ± 0.1) × 10⁶ M^?1 (25.0°C). The finding that the interaction of RibH2 with oxidized selenol is reversible with its equilibrium favored toward the reverse reaction provides an additional explanation for the exceptional mechanism of the mammalian Trx/TrxR system involving transient reduction of a disulfide bond.     

Silver‐Assisted Chemical Etching on Silicon with Polyvinylpyrrolidone‐Mediated Formation of Silver Dendrites

Metal‐assisted chemical etching (MaCE) on silicon (Si)—mediated by polyvinylpyrrolidone (PVP)—is systematically investigated herein. It is found that the morphologies and crystallographic natures of the grown silver (Ag) dendrites can be significantly modulated, with the presence of PVP in the MaCE process leading to the formation of faceted Ag dendrites preferentially along the (111) crystallographic phase, rather than along the (200) phase. Further explorations of the PVP‐mediated effect on Si etching are also revealed. In contrast to the aligned Si nanowires formed by MaCE without PVP addition, only distributed nanopores with sizes of 200 to 400 nm appear on the Si surfaces in the presence of PVP. The origin of surface polishing on Si in the PVP‐mediated MaCE process can be attributed to the distinct transport pathway of holes supplied by the Ag⁺ ions, where the holes are injected directly into the primary Ag seeds, rather than through Ag dendrites, thus leading to the isotropic etching of the Si surface.